By SDCN Editor
San Diego, CA–A new study from scientists at San Diego Zoo Wildlife Alliance published Wednesday in the Journal of Applied Ecology, found endangered mountain yellow-legged frogs being reared for release into the wild have a greater chance of survival if introduced to artificial currents at early stages of their development.
While the findings support a growing body of evidence that suggests raising bred animals in an environment similar to where they will be released can boost survival rates, the study goes even further, showing the timing of experiential exposure may be critical to successful species recovery translocations.
Led by Talisin Hammond, Ph.D., a researcher in recovery ecology at San Diego Zoo Wildlife Alliance, the study examined 256 frogs hatched from the San Bernardino Mountains in 2018. Young frogs, typically reared in settings with gentle water flow, were exposed to current simulators to mimic the experience of a mountain stream, where they would be released. After being nurtured on a diet of crickets, wax worms, fruit flies, and bean beetles, 146 young frogs were released in 2019 and closely monitored for over four months. The same methods were repeated a year later when the remaining frogs were older, and they were then introduced to the same mountain stream.
Frogs that were younger, under two years of age, grew longer limbs and became stronger swimmers when exposed to the current, and more of them ultimately survived in their native habitats. For the younger age class, strength alone did not play a significant role in whether the frogs lived after being released. Instead, researchers suspect it was due to their greater familiarity with a stream-like setting.
Breeding programs for species facing an uncertain future in their native habitats are critical for recovery, but wildlife reared in managed care can face lower success rates if translocated individuals seek out habitats more similar to what they experienced during their development.
“Exposure to naturalistic environments can help mitigate translocation challenges, but there may also be developmental windows that are the most transformative,” said Dr. Hammond. “Pre-release treatments should be tailored to these developmental windows to give wildlife the greatest chance at survival.”
The mountain yellow-legged frog is facing many threats to its survival, including habitat destruction, drought, and disease. Classified as Endangered on the International Union for Conservation of Nature Red List of Threatened Species, severe population fragmentation has led to estimates of fewer than 200 mountain yellow-legged frogs remaining in their native habitats. San Diego Zoo Wildlife Alliance and its partners are working to manage and propagate this species as part of a large-scale reintroduction effort. To date, San Diego Zoo Wildlife Alliance has released hundreds of individuals back into high-elevation mountain streams and monitored their success.